In a complete response letter (CRL) issued to Protalix, the FDA said that the drug cannot be approved until the company provides additional information related to the clinical, chemistry, and manufacturing and controls (CMC) portions of the application.

The FDA has requested additional data from a switchover trial and a long-term extension trial that was not available at the time the marketing application was originally submitted. In addition, regarding the CMC section of the application, the FDA requested information regarding testing specifications and assay validation.

Protalix noted that the agency did not request any new clinical trials of the drug.

In addition, the company pointed out that an FDA inspection of its manufacturing facilities for taliglucerase alfa, which is a plant-cell expressed form of glucocerebrosidase, found them to be acceptable. This is significant, as taliglucerase alfa is the first enzyme replacement therapy derived from a proprietary plant cell-based expression platform using genetically engineered carrot cells. Current processes used by biotech companies involve genetically engineered hamster cells grown in stainless steel tanks, which is far more costly.

Protalix said it would request a meeting with the FDA as soon as possible to determine next steps. Pfizer said it has committed to working closely with Protalix to address the requests "by providing technical, analytical and regulatory expertise."

Meanwhile, Protalix's multi-centre, double-blind paediatric trial of taliglucerase alfa will continue to enroll patients, and subjects currently enrolled in the switchover study and extension study will continue to receive the drug.

Pfizer gained worldwide licensing rights to commercialise taliglucerase alfa, excluding Israel, in a 2009 deal that called for an upfront payment to Protalix of $60m as well as potential milestone payments of up to $55m. Pfizer and Protalix agreed to split future revenues and costs relating to taliglucerase alfa on a 60-40 basis, respectively.

Gaucher disease is an inherited condition affecting around 1 in 20,000 live births. The disease is an enzyme deficiency that can lead to enlargement of the liver and spleen, excessive bleeding and bruising, anaemia, bone disease and other complications.